Embodiments of the present invention relate to a support for holding a substrate during processing.
A substrate support is used to hold a substrate, such as a silicon wafer or display, in a process chamber. The support can comprise a pedestal that receives a chuck that is capable of holding the substrate. The chuck may be a mechanical, vacuum, or electrostatic chuck. The electrostatic chuck electrostatically holds the substrate by electrostatically charging a monopolar or bipolar electrode covered by, or embedded in, a dielectric material, such as ceramic or polymer. The pedestal allows the electrical connections to the chuck to pass through and may also have fluid circulating conduits and channels to circulate a heat transfer fluid to heat or cool the substrate being held on the chuck during processing.
Newly developed plasma processes for the fabrication of integrated circuits are often performed at low, often sub-zero, temperatures or at high temperatures, which may exceed 100° C. For example, certain etching processes, such as processes used to etch low K dielectric materials, may be performed at temperatures below zero, for example, at −20 to −40° C. Conversely, processes for etching copper or platinum, or sputtering (PVD) processes, are often conducted at high temperatures of from 250 to 600° C., and temperatures used to etch aluminum may range from 100 to 200° C. It is difficult to maintain uniform temperatures across the surface of a substrate during such processes, especially when the plasma contributes to the heat load. For example, a gas plasma that is sustained by applying a power level of 2000 Watts to an inductor antenna or electrode can generate temperature variations of at least about 10° C. across a 300 mm diameter wafer. These temperature variations can have different magnitudes across the surface of the substrate.
In one method of maintaining more uniform temperatures across the substrate, heat transfer channels are distributed in the pedestal or chuck, and a cooled or heated fluid is circulated in the channels to stabilize substrate temperatures. The channels originate at a fluid inlet that receives the cooled or heated fluid, traverse the area of the support in a circuitous pathway, and terminate at a fluid outlet. However, the temperature of the support at the fluid inlet can often be hotter or colder than the temperature of the support at the fluid outlet, depending on whether the fluid receives or dissipates heat in traveling from the inlet to the outlet. In another configuration, the fluid channel loops back upon itself to form two closely abutting pathways that traverse across the area of the support. While the looped back channel reduces the inlet to outlet temperature variation, a hot or cold spot often still forms at the region of the support where the channel loops back upon itself.
Thus, it is desirable to have an apparatus capable of supporting and maintaining a substrate at uniform temperatures, especially when the substrate is processed at sub-zero or hot temperatures. It is also desirable to control the temperature of the substrate in processes that generate different heat loads, especially plasma processes.